Transformers have been used for many years to provide high voltage isolation for signals having radically different baselines, DC pedestals or other interfering low frequency artefacts. Such an isolation transformer is described in U.S. Pat. No. 6,249,171 and is used in U.S. Pat. No. 6,215,816 and applied further as an isolation amplifier in U.S. Pat. No. 4,286,225 and U.S. Pat. No. 4,360,784. Others have suggested that the coils of the transformer be integrated on or in the IC technology, such as the Analog Devices Adum1100 parts, or added into multi-layer PC boards or into hybrid modules, such as the now obsolete Analog Devices AD295 part. Problems associated with these approaches include size, reliability and application in high voltage environments.
FIG. 1 shows a multi-chip assembly 100 incorporating an embedded transformer 150 adapted to couple signals between a receiver chip 110 and a coil driver chip 120 according to the prior art. The two chips or dies are electrically connected to the lead frame 140 of the packaged device 100. The transformer 150 comprises two coils which are embedded in an insulating material 130 such as PCB material, as will be appreciated by those skilled in the art. These devices find application in situations where very high voltages (fixed or time varying) may be present and the designer desires to transfer low voltage signals out of this “hostile” environment into a well controlled voltage supply environment where, for example, digital signal processing can take place. In order to couple signals between these two environments, one common solution is to use coupling capacitors or discrete transformers or embedded transformers such as that shown in FIG. 1.
Alternative techniques use opto-electronic components as an interface between the two chips requiring a communication channel. These devices are based on a light signal transmitted from one side of the voltage divide to the other. Problems with such architectures include the power requirements of such opto-electronic components and the restriction in application to those possible using such technology.
There is therefore a need for an improved integrated package including two or more chips having a transformer interface provided therebetween.